The present invention relates to a clamping device that increases the diameter of a gripping assembly that is inserted into a hole in a workpiece and thus grips the inner circumferential surface of the hole, and particularly relates to such a clamping device that is adapted so that, in the vicinity of a scraper, no clearance occurs between the gripping assembly and a clamp rod, and the scraper.
From the past, clamping devices of various types (so called hole clamps or expansion clamps) have been put into practical use, with which it is arranged, by expanding the diameter of a grip claw section of a gripping assembly that has been inserted into a hole in a workpiece as by a clamp rod, to grip the inner circumferential surface of the hole and to pull the workpiece towards the clamp main body so as to clamp it.
For example, the clamping device described in Patent Document #1 comprises a clamp main body, a gripping assembly, a clamp rod for increasing the diameter of the gripping assembly, a hydraulic cylinder that drives the clamp rod. The gripping assembly comprises four grip forming members, and grip claw sections are formed on these grip forming members, with their cross sectional shapes orthogonal to the axis of the clamp rod being formed as flattened letter D shapes. With regard to a lower portion and an intermediate portion of the clamp rod, the cross sectional shapes orthogonal to the axis of the clamp rod are formed as circular rod shapes, and a tapered section is formed at the upper end portion of the clamp rod, having an inverted four cornered conical shape whose diameter becomes progressively larger upwards. Base end flange portions are formed at the lower ends of the grip forming members, and also a guidance and support mechanism is provided to the clamp main body that guides and supports the base end flange portions of the grip forming members so that they are shiftable in the horizontal direction.
Moreover, in Patent Document #2, there are provided a clamp main body, a one piece annular collet (i.e. a gripping assembly), a pull rod (i.e. a clamp rod), a hydraulic cylinder that drives the pull rod. The collet is made so as to be capable of being elastically deformed so that its external diameter increases, due to a single vertically oriented slit therein.
Since, with this type of clamping device, the upper end portions of the gripping assembly and the clamp rod are constructed so as to be inserted through a through hole in the upper end portion of the clamp main body and to extend upwards, accordingly, in known Patent Document #3 filed by the applicant of the present application, in order for foreign matter such as swarf or the like not to be allowed to enter into the interior of the clamping device through an annular clearance between the through hole and the outer circumferential surfaces of the gripping assembly and the clamp rod, it has been proposed for the clamping device to include a scraper provided to the clamp main body and having a certain flexibility, so as to block up the annular clearance described above.
With this clamping device, the gripping assembly is divided into sections by four slits so as to form four grip forming members, and the clamp rod has an intermediate rod section whose cross section is circular and a tapered section that extends at the upper end of this intermediate rod section. The tapered section is formed with four tapered surfaces that contact against grip claw sections of the four grip forming members.    Patent Document #1: German Patent 4, 020, 981.    Patent Document #2: Japanese Laid Open Patent Publication Heisei 11-188551.    Patent Document #3: Japanese Laid Open Patent Publication 2010-125537.
With the clamping device of Patent Document #3, the workpiece is pulled towards the clamp main body after the clamp rod has been driven downwards for clamping, after the diameter of the four grip forming members has been increased, and after the inner circumferential surface of the hole in the workpiece has been gripped. When the external diameter of these four grip forming members is increased, the slits between the grip forming members are enlarged, and those four slits remain open.
Moreover, when the clamp rod moves relatively downwards with respect to the gripping assembly, not only is the clearance between the four grip forming members and the clamp rod enlarged (i.e.“internal clearance”), but also, in the vicinity of the scraper, the cross section of the gripping assembly and the clamp rod (i.e. the cross section orthogonal to the axis of the clamp rod) becomes non circular.
For this reason, not only is it not possible to block the four slits described above and the internal clearance described above with the scraper, but also a clearance appears between the external periphery of the gripping assembly and the clamp rod and the scraper (i.e. “outer peripheral clearance”), and it is not possible to block this outer peripheral clearance adequately by the scraper.
Due to the above, when the clamped workpiece is subjected to machining, foreign material such as swarf and so on may enter through the various clearances described above into the interior of the clamping device, and this causes faults of the clamping device.
On the other hand, in order to prevent ingress of foreign material such as swarf during machining, pressurized air used to be supplied to the interior of the clamp main body, so that this pressurized air is ejected from the various clearances described above. However, since the various clearances described above are large, the level of consumption of pressurized air becomes great, and the cost of supplying this pressurized air becomes high.
Moreover, there is the problem that the edge portions in the widthwise direction of the grip claw sections of the grip forming members may bite into the scraper and may damage the scraper, so that the durability of the scraper is remarkably decreased.
On the other hand, sometimes a compact clamping device is needed, since in some cases the diameter of the hole formed in the workpiece for clamping is about 6 mm. In the case of such compact clamping device, the external diameter of the grip claw sections of the gripping forming members also becomes about 6 mm, so that the diameter of the cross section of the clamp rod is about 2 or 3 mm. Since, with such compact clamping device, the diameter of the intermediate section of the clamp rod (horizontal cross section is circular) thus becomes extremely small, accordingly it becomes difficult to ensure that the clamp rod has sufficient pulling strength for driving the clamping action.
The objects of the present invention are to present a clamping device that is capable of enhancing the durability of a scraper, to present a clamping device that is capable of reducing the amount of pressurized air consumed by blowing, to present a clamping device that is capable of ensuring the strength of a clamp rod against pulling, and so on.